Miniature sounder with multi-part tuned cavities

ABSTRACT

A miniature sounder having a diaphragm closing one end of a tuned chamber. The other end of the chamber communicates with the interior of a tuned housing through which an open-ended enclosure extends. The oscillating frequency of the diaphragm. The housing and enclosure are tuned to resonate at the desired frequency.

BACKGROUND OF THE INVENTION

The present invention relates to miniaturized sounders and in particularto a buzzer for a pocket paging device or the like.

Pocket pagers have gained wide use and acceptance in recent years. Suchpages are commonly used by physicians, repair technicians, and otherswho must remain in contact with a central location. The pager, whichcorresponds in size roughly to that of a cigarette package, is carriedin a pocket or clipped to the clothing of the user. In one common typeof paging system, a radio signal at a particular frequency is generatedwhen contact with the user is required. The radio signal serves totrigger an oscillator within the pager which, in turn, drives a buzzer.The user, upon hearing the buzzer, places a telephone call to thecentral location to receive his message.

Pocket pagers must be small enough to be comfortably carried by theuser. In addition, the pager must be large enough to contain the buzzeralong with its associated electronics and power supply. It is thusdesirable to miniaturize the components of the pager as much aspossible. This poses a particular problem with regard to the actualsounder since it must be capable of generating a sound sufficiently loudto insure attracting the user's attention regardless of ambiant noiseconditions.

Heretofore, various attempts have been made to produce such miniaturesounders or buzzers. In one such attempt, a folded horn is positionedwithin a tuned cavity. This, however, requires precise tuning of thebuzzer components. In our co-pending application Ser. No. 236,001 filedFeb. 19, 1981 for MINIATURE SOUNDER WITH DOUBLE TUNED CAVITY, a sounderis provided which relies on the tuning of cavities within the sounderhousing. A problem of these prior art devices is that since the soundercomponents are tuned to a particular frequency, in the event of afrequency shift the output will deteriorate. This may or may not bedesirable depending upon the ultimate use of the sounder. The "Q" of thesounder is a measure of the sensitivity of the sounder to frequencyshift. The lower the Q, the less susceptible the sounder output will beto variations in the drive frequency.

In view of the above, it is the principal object of the presentinvention to provide an improved sounder which is small in volume,capable of producing a relatively loud, audible sound and in which the Qmay be controlled to some extent as required for particular usages.

A further object is to provide such a sounder which is compatible withconventional pocket pager drive circuits and power sources.

A still further object is to provide such a sounder which is reliable,efficient and which may be constructed of a small number of componentswhich may be readily assembled.

SUMMARY OF THE INVENTION

The above and other beneficial objects and advantages are attained byproviding a miniature sounder comprising a double tuned cavity resonatorin which the Q value of the resonator may be altered by varying theratio of components of the cavities.

The sounder includes a diaphragm disposed within a housing. Anopen-ended, two portion chamber extends from the diaphragm. Anopen-ended enclosure extends into the housing. The volume of the chamberand the combined volumes of the housing and enclosure are tuned to thedesired harmonic of the drive frequency of the diaphragm. By varying theratio of the enclosure volume to housing volume and/or chamber firstportion to chamber second portion variation in the Q of the sounder maybe obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view of a miniature sounder in accordance withthe present invention;

FIG. 2 is a bottom plan view of the sounder of FIG. 1;

FIG. 3 is a sectional view along reference lines 3--3 of FIG. 1 in thedirection of the arrows; and,

FIG. 4 is a sectional view along reference lines 4--4 of FIG. 1 in thedirection of the arrows.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is now made to the drawings and to FIG. 1 in particularwherein a miniature sounder 10 in accordance with the present inventionis depicted. The sounder 10 is contained within a generally cubichousing 12 formed of a suitable material such as ABS plastic or thelike. The sides of housing 10 are approximately 0.535" by 0.555" and theheight of the unit is approximately 1/2".

A pair of connectors 14 extend from the bottom of the housing where theyengage the contacts 16 of a solder patch 18. The ends of a coil aresimilarly connected to the solder patch thereby permitting the coil tobe activated through connectors 14. The connectors 14 facilitate seatingand securing the sounder 10 into a socket in the pocket pager assemblyor other device with which the sounder is to be used and also serve tomake electrical contact with an oscillator forming a part of the pagerdrive circuit. Such pagers are well known and are well defined in theart and form no part of the present invention.

Referring now to FIG. 3, it can be noted that there is contained at thebottom of the housing a driver generally designated 20. The driver 20 isof a conventional construction and may, for example, be constructed inaccordance with the teachings of our commonly assigned U.S. Pat. No.4,251,807 for MINIATURE BUZZER. In brief, the driver 20 consists of aplastic support collar 22 in which a pole piece 24 of a magneticmaterial is supported. A coil 26 is disposed about the pole piece. Theends of the coil 26 are drawn through the bottom of the unit forconnection with contacts 14 through the solder patch 18 as described. Aring magnet 28 surrounds the coil with its upper edge defining a commonplane with the top of the pole piece.

A diaphragm 30 formed of a tempered magnetic material is positionedwithin collar 22 spaced above the top edge of the pole piece 24. Anarmature 32 of magnetic material is spot welded to the rear of thediaphragm (i.e., opposite to the pole piece). The diameter of thearmature is less than that of the diaphragm but large enough to span theinner diameter of ring magnet 28. The diaphragm 30 fits onto a step 34formed in collar 22. A closure plate 36 fits on a lower step 38 formedat the top of collar 22. A hollow tube 40 extends upwardly from anopening through plate 36. Thus, the upper portion 42 of collar 22 (i.e.,above step 34) along with the bore 44 of tube 40 define an open-endedchamber 46 the bottom end of which is closed by the diaphragm 30 and thetop end of which communicates with the interior 48 of housing 12.Chamber 46 is made up of two portions, a first portion 50 (occupying avolume V₁) between the diaphragm 30 and plate 36 and a second portion 52(occupying a volume V₂) comprising the interior of tube 40.

An open-ended enclosure 54 in the form of a tube extends from the bottom56 of housing 12 into the housing interior. The interior 58 of enclosure54 occupies a volume V₄ determined by its height and diameter. Thehousing interior 48 occupies a volume V₃ determined by its dimensions.

By varying the diameter of collar 22 above diaphragm 30 and/or thedistance between diaphragm 30 and plate 36 and/or the diameter andlength of tube 40 the volume of the chamber and hence its resonantfrequency may be altered. Similarly the resonant frequency of thehousing may be altered by varying the dimensions of the sides or theheight of the housing. Thus, the volume of the chamber and the combinedvolume of the housing and enclosure may be tuned to the frequency or aharmonic of the oscillator driving diaphragm 30.

In a successful practice of the invention wherein the diaphragm wasoscillated at approximately 2000 Hz chamber 46 was tuned to 6000 Hz andthe interior 48 of housing 12 and enclosure 54 were tuned to 2000 Hz.Enclosure 54 was 0.125" long and had a diameter of 0.135". To vary the Qof the system the ratio V₁ /V₂ and/or the ratio V₄ /V₃ can be varied.Reducing either ratio lowers the Q of the unit thereby making theloudness of the output sound less dependent on slight variations in thedrive frequency. Conversely, it if were desirable to raise the Q of theunit one or both of the above ratios could be increased.

Thus, in accordance with the above, the aforementioned objects areattained.

Having thus described the invention, what is claimed is:
 1. A miniaturesounder comprising:a diaphragm; a surrounding housing disposed aboutsaid diaphragm; an open-ended chamber dimensioned to resonate at apredetermined frequency positioned within said housing, said chamberhaving a first portion including a first open end closed by saiddiaphragm and a second portion including an opposite open endcommunicating with the interior of said housing; an armature affixed tosaid diaphragm; a magnetic circuit operatively connected to saidarmature for driving said diaphragm at a desired frequency; and, anopen-ended enclosure positioned within said housing providing an outletfrom said sounder; said open-ended chamber having a volume tuned to asubharmonic of said desired frequency and said open-ended enclosure andhousing having a combined volume tuned to said desired frequency.
 2. Theminiature sounder in accordance with claim 1 wherein said chamber has aresonant frequency substantially three times said desired frequency. 3.The miniature sounder in accordance with claim 1 or 2 wherein saidenclosure comprises a tube.
 4. The miniature sounder in accordance withclaim 1 wherein said diaphragm frequency comprises approximately 2070Hz, said chamber is tuned to a resonant frequency of approximately 6200Hz, and said housing and enclosure combined are tuned to a resonantfrequency of approximately 2070 Hz.
 5. The miniature sounder inaccordance with claim 1 wherein said housing is cubical.